Semiconductor ignition system



March 1, 1966 L. R. HETZLER ETAL 3,237,620

SEMICONDUCTOR IGNITION SYSTEM Filed Aug. 28, 1963 INVENTOR5 LEWIS R.HETZLER BROOKS H.5H RT THEIR ATTORNEY United States Patent 3,237,620SEMICONDUCTOR IGNITION SYSTEM Lewis R. Hetzl-er and Brooks H. Short,Anderson, Ind., assignors to General Motors Corporation, Detroit, Mich.,a corporation of Delaware Filed Aug. 28, 1963, Ser. No. 305,098 14Claims. (Cl. 123-148) This invention relates to a semiconductor ignitionsystem and more particularly to a semiconductor ignition system whichhas the feature of reducing the amount of power required to operate it.

In certain types of semiconductor ignition systems, it has been wellknown practice to connect a semiconductor such as a transistor in serieswith the primary winding of an ignition coil. The conduction of thesemiconductor is controlled in synchronism with operation of the engineby breaker contacts, magnetic pick-ups or by other suitable means. Insome of these ignition systems, the semiconductor such as the transistoris normally biased to conduct by the battery and is only turned off forshort periods of time when ignition is required.

Although these systems provide good ignition timing, they have thedis-advantage that the on time of the transistor is such that aconsiderable amount of current may be wasted. Thus when the engine isoperating at low speed, the transistor or semiconductor may be turned onfor a length of time that is greater than that required for properbuild-up of magnetic flux in the ignition coil with a consequent wasteof power.

In contrast to the above described ignition systems, it is an object ofthis invention to provide an ignition system wherein the interval oftime that the primary circuit of the ignition coil is energized ismaintained substantially constant at both high and low speeds of theengine.

Still another object of this invention is to provide a semiconductorignition system wherein a semiconductor such as a transistor controlsthe current flow through the primary winding of an ignition coil andwherein means are provided for maintaining the on time of thesemiconductor or transistor substantially constant at different enginespeeds.

A further object of this invention is to provide a semiconductorignition system wherein a semiconductor such as a transistor controlsprimary winding current and wherein this transistor or semiconductor isswitched on by an engine driven timing device and is switched off by anelectric timing circuit which maintains a predetermined constant timeinterval between the turn-on and turn-off of the semiconductor.

Still another object of this invention is to provide a semiconductorignition system wherein a semiconductor such as a transistor controlsprimary winding current and wherein the semiconductor is triggered intoconduction by a magnetic pick-up device and is switched off at apredetermined time interval following its beginning of conduction by anRC timing circuit which provides a constant time interval of turn-onregardless of the speed that the magnetic pick-up is driven.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings wherein preferred embodiments of the present invention areclearly shown.

The single figure drawing is a schematic circuit diagram of asemiconductor system made in accordance with this invention.

Referring now to the drawing, the reference numeral generally designatesan ignition coil which is used to provide ignition pulses for aninternal combustion engine. The ignition coil 10 has a primary winding12 "ice and a secondary winding 14 which are magnetically coupled in theusual manner. One side of the secondary winding 14 is connected directlyto ground as shown. The opposite side of the secondary winding 14 isconnected with a rotor contact 16 which cooperates with the electrodes18 of a conventional distributor cap 20.

The rotor contact 16 is driven by the engine 22. The electrodes 18 ofthe distributor cap 20 are connected respectively with one side of thespark plugs 24 which are used to ignite the combustible mixture of theinternal combustion engine 22. In the drawing, a four cylinder enginehas been shown but it will be appreciated that this invention can beused with engines having six, eight or more cylinders.

The ignition system of this invention employs a semiconductor switchmeans which in this case takes the form of an NPN transistor 26. Thecollector electrode of transistor 26 is connected with junction 28 whichis also connected to one side of the primary winding 12. The emitterelectrode of transistor 26 is connected with junction 30. A diode 32 isconnected between junction 30 and ground and it is seen that a capacitor34 connects the junctions 28 and 30 and is therefore connected acrossthe emitter and collector electrodes of the transistor 26.

The ignition system has another semiconductor switch means which takesthe form of an NPN transistor 36. The collector electrode of transistor36 is connected with junction 38. A resistor 40 is connected betweenjunctions 38 and 42. The junction 42 is connected with the baseelectrode of transistor 26 and a resistor 44 is connected betweenjunction 42 and ground.

The emitter electrode of transistor 36 is connected directly to groundas shown. The base electrode of transistor 36 is connected with junction46. The junction 46 is connected with junction 48 via the conductor 50.A capacitor 52 is connected between the junctions 48 and 28.

The direct current power source for the ignition system of thisinvention is illustrated as a battery 54. The negative side of thebattery is connected to ground whereas the positive side of the batteryis connected to one side of a manually operable ignition switch 56. Theopposite side of the ignition switch is connected with conductor 58.

A resistor 60 is connected between conductor 58 and the junction 48.Another resistor 62 connects the conductor 58 with the junction 38. Aresistor 64 connects the conductor 58 with one side of the primary 12 ofthe ignition coil 10.

Although the direct current source 54 has been shown as a battery, itwill be appreciated that on passenger cars and on certain othervehicles, a generator is provided which supplies ignition power andcharges the battery when the engine is being driven at a predeterminedspeed. When cranking the engine, the battery 54 supplies the ignitionpower and will supply ignition power when the generator does not developa voltage sufiicient to charge the battery.

The ignition system of this invention has an engine driven timing devicegenerally designated by reference numeral 70. This ignition timingdevice includes a rotor 72 which is formed of magnetic material andwhich is driven by the engine 22. The four arms of the rotor 72 controlthe flow of magnetic flux through a core element 74 which is formed ofmagnetic material. A pick-up coil 76 is wound on the core 74 andmagnetic flux is caused to flow through the magnetic core 74 by a sourceof magnetic flux which takes the form of a permanent magnet 78.

In actual practice, the magnetic pick-up 70 and the distributor cap 20may be built into one unit and rotation of the motor contact 16 issynchronized with the rotation of the rotor 72 and both of theseelements are driven by the engine 22.

It will be appreciated that as the rotor 72 rotates, the reluctance ofthe magnetic circuit is varied depending upon whether or not the arms ofthe rotor are aligned with the tips 78a and 78b of the core 74. Thevoltage that is induced in the pick-up coil 76 will therefore vary asthe ends of the arms of the rotor 72 become aligned and then go out ofalignment with the tips 78a and 78b of the core 74. The voltage that isgenerated in the pick-up coil 76 will be an alternating voltage due tovariation in the reluctance of the magnetic cricuit as the rotor 72rotates.

One side of the pick-up coil 76 is connected to ground as shown whilethe opposite side of this pick-up coil is connected to one side of adiode 80. The opposite side of the diode 80 is connected with junction46.

When the ignition switch 56 is closed, the ignition sys tem of thisinvention is energized. Current can now flow from conductor 58, throughresistor 60, through junction 48, through conductor 50, through junction46, through diode 80 and then through the pick-up coil 76 to ground.Assuming that there is no voltage generated at this time in the pick-upcoil 76, the transistor 36 will be biased to a conductive condition inits emitter-collector circuit because the junction 46 is positive withrespect to ground due to' the voltage drop across diode 80 and thepick-up coil 76. When the transistor 36 switches on in itscollector-emitter circuit, current flows from conductor 58, throughresistor 62, and then through the collector-emitter circuit of thetransistor 36 to ground. The resistor 62 limits the current flow to apredetermined value through the transistor 36.

With transistor 36 in a conductive condition, the junction 42 and thebase of transistor 26 will be at a potential which biases the emitterand base electrodes of the transistor 26 such that the transistor 26will be nonconductive in its collector-emitter circuit and no currentcan flow under this condition through the primary winding 12.

When the transistor 36 is biased to conduct as when the junction 46 ispositive with respect to ground, the capacitor 52 will be charged withthe polarity indicated on the drawing. The charging circuit for thecapacitor is from conductor 58, through resistor 64, through primarywinding 12, through the capacitor 52, through junction 48, throughconductor 50 and then through the base-emitter circuit of transistor 36.It can be seen from the foregoing that when the transistor 36 is biasedto a conductive condition by the battery 54, the capacitor 52 has anopportunity to charge to a potential of the polarity shown on thedrawing.

As the rotor 72 rotates, the time will come when a pulse of voltage isgenerated in the pick-up coil 76 which is positive on its grounded sideand negative on its side connected with the cathode of diode 80. Avoltage of this :polarity will drive the emitter of transistor 36positive with respect to its base or at least equal to the potential ofits base to cause the transistor 36 to switch off in itsemitter-collector circuit. When the transistor 36 switches off in itscollector-emitter circuit, current will flow from conductor 58, throughresistor 62, through resistor 40 and then through resistor 44 to ground.In effeet, the resistors 62, 40 and 44 are now a voltage divider and avoltage drop will be developed across resis tor 44 which is positive atjunction 42. The voltage developed across resistor 44 will bias thetransistor 30 to its conductive state between its collector and emitterand current can flow from conductor 58, through resistor 64, throughprimary 12, through junction 28, through the collector-emitter circuitof transistor 26 and then through the diode 32 to ground.

From the foregoing, it can be seen that current will begin to flowthrough the primary winding 12 whenever a voltage is induced in thepick-up coil 76 which is of such a polarity as to switch off thetransistor 36 and switch on the transistor 26.

The transistor 36 will continue to be switched off and the transistor 26will continue to be switched on even though the voltage in the pick-upcoil 76 now goes to zero or reverses. The transistor 36 is maintained ina nonconductive condition by the potential accumulated by the capacitor52 of the polarity shown on the drawing. Thus, the charge on thecapacitor 52 is such as to drive the base of transistor 36 negative tomaintain it in a nonconductive condition for a predetermined length oftime.

The length of time that the transistor 36 can be maintainednonconductive and the transistor 26 conductive is determined by thevalues of the resistor 60 and the capacitor 52 and is determined by theRC time constant of these two elements. The capacitor 52 dischargesthrough the collector-emitter circuit of transistor 26, through diode32, through battery 54, through the ignition switch 56 and then throughthe resistor 60 to the opposite side of the capacitor 52. When theenergy stored in the capacitor 52 has been dissipated to the point wherethe junction 46 goes positive with respect to ground, the transistor 36will be switched back on causing the transistor 26 to be immediatelyswitched oif. When transistor 26 switches off, a high voltage is inducedin the secondary winding 14 which causes one of the spark plugs 24 to befired through the rotor contact 16 and one of the distributor electrodes18.

From the foregoing, it will be apparent that transistor 26 is switchedon when a voltage of the proper polarity is induced in the pick-up coil76. The transistor 26 is then not switched oil until the chargeaccumulated by the capacitor 52 has been reduced to a predeterminedvalue. Since the discharging time of capacitor 52 is constant asdetermined by the RC time constant of the resistor 60 and the capacitor52, the time interval that the transistor 26 is switched on will remainconstant to provide a constant on time for the primary circuit of theignition system regardless of engine speed.

It will be appreciated that the switching on of the transistor 26 isinitiated by the generation of a voltage in the pick-up coil 76 of theproper polarity and is terminated at a fixed time after initiation asdetermined by the RC time constant of resistor 60 and capacitor 52. Themagnetic pick-up 70 therefore has no etiect in terminating the on timeof the transistor 26 since this is accomplished by the electric RCtiming circuit.

The output voltage of the magnetic pick-up 70 must have pulses that arespaced a suflicient interval of time which is at least as great as theconstant on time of the transistor 26. In other words, once thetransistor 26 is switched on, the system should operate to maintain thistransistor switched on for a time determined by the RC time constant ofresistor 60 and capacitor 52. During this interval of time, it isimportant that no voltage pulses be induced in the pick-up coil 76 thatmight switch the transistor 36 off and prolong the time interval thattransistor 26 is switched on over and above the time set by resistor 60and capacitor 52. For this reason, it is important that the pulsesdeveloped in pick-up coil 76 which switch transistor 36 off be spaced intime an amount greater than the RC time constant of the resistor 60 andcapacitor 52.

The diode 80 being connected in series with the pickup coil 76 preventsvoltage pulses which are negative at ground and positive at the cathodeof diode 80 from triggering the transistor 36.

While the embodiments of the present invention as herein disclosed,constitute a preferred form, it is to be understood that other formsmight be adopted.

What is claimed is as follows:

1. An ignition control unit adapted to be connected with the primary ofan ignition coil, with an engine driven timing device and with a sourceof direct current comprising, first and second transistors, said firsttransistor being adapted to be connected in series with the primarywinding of an ignition coil, means interconnecting said transistorswhereby said first transistor is driven conductive when said secondtransistor is biased to a nonconductive condition, said secondtransistor being adapted to be connected with an engine driven timingdevice which is capable of causing said second transistor to be biasedto a nonconductive condition, and a timing circuit connected with saidsecond transistor for causing said second transistor to remain in anonconductive condition for a predetermined fixed time following thebiasing of said second transistor to its nonconductive state.

2. The ignition control unit according to claim 1 wherein the timingcircuit includes a resistor and capacitor having apredetermined RC timeconstant.

3. The ignition control unit according to claim 1 wherein the baseelectrode of the first transistor is connected with the collectorelectrode of the second transistor.

4. An ignition system for an internal combustion engine comprising, anignition coil having a primary winding and a secondary winding,.a sourceof direct current, a first transistor having emitter, collector and baseelectrodes, means connecting the emitter and collector electrodes ofsaid first transistor in series with said primary winding of saidignition coil and in series with said source of direct current, a secondtransistor having emitter, collector and base electrodes, an enginedriven timing device connected with the base electrode of said secondtransistor and operative to cause said second transistor to be biased toa nonconductive condition, an RC timing circuit energized from saidsource of direct current when said second transistor is biased to aconductive state, said RC timing circuit being connected with the baseelectrode of said second transistor whereby said second transistor ismaintained in a nonconductive condition for a predetermined length oftime once it is switched to this condition by said engne driven timingdevce, and means connecting the collector electrode of said secondtransistor with the base electrode of said first transistor.

5. An ignition system for an internal combustion engine comprising,first and second transistors, an ignition coil having a primary windingand a secondary winding, a source of direct current, means connectingthe emitter and collector electrodes of said first transistor in serieswith said source of direct current and in series with said primarywinding of said ignition coil, an engine drven timing device, meansconnecting the emitter and base electrodes of said second transistorwith said engine driven timing device, a first circuit connected acrosssaid source of direct current including the emitter and collectorelectrodes of said second transistor, a second circuit connected inparallel with the emitter and collector electrodes of said secondtransistor, means connecting the base electrodes of said firsttransistor with said second circuit, and an RC timing circuit connectedwith the base electrode of said second transistor for maintaining saidsecond transistor in a nonconductive condition for a time correspondingto the RC time constant of said RC timing circuit and following thebiasing of said second transistor to its nonconductive state by saidengine driven timing device.

6. An ignition system for an internal combustion engine, first andsecond transistors each having emitter, collector and base electrodes,an ignition coil having a primary winding and a secondary winding, asource of direct current, means connecting said primary winding and theemitter and collector electrodes of said first transistor in series withsaid source of direct current, an engine driven magnetic timing devicehaving an output coil, a diode, a first current path connected acrosssaid source of direct current including the collector and emitterelectrodes of said second transistor, a second current path connectedacross said source of direct current including in a series connectionsaid diode and said output coil, said diode and output coil beingconnected across said base and Q emitter electrodes of said secondtransistor, means connecting the collector electrode of said secondtransistor with the base electrode of said first transistor, and acapacitor connecting the base electrode of said second transistor andthe collector electrode of said first transistor, said capacitor beingcharged through the primary winding of said ignition coil and throughthe emitter and base circuit of said second transistor when said secondtransistor is biased to a conductive condition by the voltage generatedin said output coil, the voltage accumulated by said capacitormaintaining said second transistor in a nonconductive condition for apredetermined fixed time following the biasing of said second transistorto its nonconductive condition by the voltage generated in said outputcoil.

7. An ignition system for an internal combustion engine comprising,first and second transistors, an ignition coil having a primary windingand a secondary winding, a source of direct current, a magnetic pick-updevice having an output coil driven by said engine, means connectingsaid primary winding, the emitter and collector electrodes ofsaid firsttransistor and said source of direct current in a series circuit, meansconnecting said first and second transistors in such a manner that saidfirst transistor is switched to a conductive state when said secondtransistor is switched to a nonconductive state, means connecting saidoutput coil with said second transistor, and an electric timing circuitfor maintaining said second transistor in its nonconductive state afterit has been switched to this state by a voltage generated in said outputcoil, said timing circuit maintaining said second transistor in itsnonconductive state for a fixed time which is independent of enginespeed.

8. The ignition system according to claim 7 wherein the electric timingcircuit is an RC network.

9. The ignition system according to claim 7 wherein the electric timingcircuit includes a capacitor which is connected between the baseelectrode of said second transistor and a circuit that connects thecollector electrode of the first transistor and one side of the primarywinding of said ignition coil.

10. The ignition system according to claim 7 wherein a diode and saidoutput coil are connected across said emitter and base electrodes ofsaid second transistor.

11. An ignition system for an internal combustion engine comprising,first and second conductor means adapted to be connected with a sourceof direct current, an ignition coil having a primary winding and asecondary winding, a semiconductor switching device, means connectingsaid primary winding and said semiconductor switching in series acrosssaid conductors, an engine driven control means, a bias circuitcontrolled in synchronism with operation of said engine driven controlmeans connected with said semiconductor switching device, said biascircuit being operative to bias said semiconductor switching device to aconductive condition when said engine driven control means is in a predetermined position, and a timing circuit coupled to said bias circuit,said timing circuit being operative through said bias circuit tomaintain said semiconductor switching device in a conductive conditionfor a predetermined fixed length of time following the initiation of itsconduction and independently of engine speed.

12. An ignition system for an internal combustion engine comprising,first and second conductor means adapted to be connected across a sourceof direct current, an ignition coil having a primary winding, first andsecond semiconductor switching devices, means connecting said firstsemiconductor switching device and said primary winding in series andacross said source of direct current, a first bias circuit for saidfirst semiconductor switching device connected across said conductormeans and operative to bias said first semiconductor switching device toa nonconductive condition, a second biasing circuit for said secondsemiconductor switching device connected across said conductor means andoperative to bias said second semiconductor switching device to aconductive condition, means interconnecting said first semiconductorswitching device and said second switching device whereby said firstsemiconductor switching device is switched to a conductive condition'when said second semiconductor switching device is biased to anonconductive condition, means driven in synchronism with said enginefor periodically biasing said second semiconductor switching device to anonconductive condition, and a timing circuit including a capacitor formaintaining said second semiconductor switching device nonconductive fora predetermined length of time following the biasing of said secondsemiconductor switching device to its nonconductive state.

13. An ignition system for an internal combustion engine comprising,first and second conductor means adapted to be connected across a sourceof direct current, an ignition coil having a primary winding, first andsecond transistors, means connecting the emitter and collector of saidfirst transistor and said primary winding of said ignition coil in'series with said conductor means, a biasing circuit connected acrosssaid conductor means and with the emitter and base of said firsttransistor for periodically biasing said first transistor to anonconductive condition, means connecting the emitter and collector ofsaid second transistor across said conductor means and in parallel withsaid biasing circuit, said second transistor when conductive shuntingsaid biasing circuit to thereby bias said first transistor to anonconductive condition, means connected with the emitter and base ofsaid second transistor including means driven in synchronism with saidengine 'for controlling the conduction of said second transistor, and acapacitor connected between the base of said second transistor and oneof the emitter and collector electrodes of said first transistor, saidcapacitor being charged across said conductor means by current flowthrough the emitter-base circuit of said second transistor and beingdischarged through the emitter-collector circuit of said firsttransistor, said capacitor when discharging being operative to hold saidsecond transistor in its nonconductive state for a length of timedetermined by the rate of discharge of said capacitor.

14. An ignition system for an internal combustion engine comprising, asource of direct current, first and second conductor means connectedacross a source of direct current, a semiconductor switching device, anignition coil having a primary winding and a secondary winding, meansconnecting said semiconductor switching device and said primary windingin series across said conductor means, a biasing circuit connected withsaid conductor means and with said semiconductor switching device forbiasing said semiconductor switching device to a nonconductive conditionby said source of direct current, engine driven control means, and acontrol circuit coupling said engine driven control means and saidsemiconductor switching device, said control circuit being operative toperiodically trigger said semiconductor switching device to a conductivecondition, and timing means coupled to said control circuit andoperative to maintain said semiconductor switching device in aconductive condition for a predetermined fixed time following thebeginning of its conductive cycle and independently of engine speed.

References Cited by the Examiner UNITED STATES PATENTS 2,811,672 10/1957Gilbert 123148 3,087,090 4/1963 Konopa 123148 MARK NEWMAN, PrimaryExaminer. RICHARD B. WILKINSON, Examiner.

1. AN IGNITION CONTROL UNIT ADAPTED TO BE CONNECTED WITH THE PLURALITY OF AN IGNITION COIL, WITH AN ENGINE DRIVEN TIMING DEVICE AND WITH A SOURCE OF DIRECT CURRENT COMPRISING, FIRST AND SECOND TRANSISTORS, SAID FIRST TRANSISTOR BEING ADAPTED TO BE CONNECTED IN SERIES WITH THE PRIMARY WINDING OF AN IGNITION COIL, MEANS INTERCONNECTION SAID TRANSISTORS WHEREBY SAID FIRST TRANSISTOR IS DRIVEN CONDUCTIVE WHEN SAID SECOND TRANSISTOR IS BIASED TO A NONCONDUCTIVE CONDITION, SAID SECOND TRANSISTOR BEING ADAPTED TO BE CONNECTED WITH AN ENGINE DRIVEN TIMING DEVICE WHICH IS CAPABLE OF CAUSING SAID SECOND TRANSISTOR TO BE BIASED TO A NONCONDUCTIVE CONDITION, AND A TIMING CIRCUIT CONNECTED WITH SAID SECOND TRANSISTOR FOR CAUSING SAID SECOND TRANSISTOR TO REMAIN IN A NONCONDUCTIVE CONDITION FOR A PREDETERMINED FIXED TIME FOLLOWING THE BIASING OF SAID SECOND TRANSISTOR TO ITS NONCONDUCTIVE STATE. 